Dimethyl ether fuel compositions and uses thereof

ABSTRACT

The present invention provides useful fuel compositions which may be produced substantially from renewable resources, such as biomass, to provide green fuel compositions, methods, and systems. In some embodiments, fuel compositions include dimethyl ether and one or more C 2  or larger alcohol, such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, or tert-butanol. In some embodiments, fuel compositions include dimethyl ether and one or more C 2  or larger hydrocarbons, such as propane, propylene, propyne, and propadiene, n-butane, isobutane, isobutylene, 1-butene, 2-butene, or 1,3-butadiene. Methods of making these novel DME-based fuel compositions, particularly from biomass-derived syngas, are described. Various applications and methods of using the fuel compositions, such as portable cylinder fuels for camping, are disclosed. Additionally, principles of burner design for these fuel compositions are disclosed herein.

PRIORITY DATA

This patent application claims priority under 35 U.S.C. §120 from U.S. Provisional Patent Application Nos. 61/410,965; 61/410,967; and 61/410,968, each filed Nov. 8, 2010, the disclosures of which are hereby incorporated by reference herein for all purposes.

FIELD OF THE INVENTION

This invention generally relates to the field of fuel compositions that include dimethyl ether, as well as apparatus to store and combust such fuel compositions.

BACKGROUND OF THE INVENTION

Synthesis gas (hereinafter referred to as syngas) is a mixture of hydrogen (H₂) and carbon monoxide (CO). Syngas can be produced, in principle, from virtually any material containing carbon. Carbonaceous materials commonly include fossil resources such as natural gas, petroleum, coal, and lignite; and renewable resources such as lignocellulosic biomass and various carbon-rich waste materials. It is preferable to utilize a renewable resource to produce syngas because of the rising economic, environmental, and social costs associated with fossil resources.

Syngas is a platform intermediate in the chemical and biorefining industries and has a vast number of uses. Syngas can be converted into alkanes, olefins, oxygenates, and alcohols. These chemicals can be blended into, or used directly as, diesel fuel, gasoline, and other liquid fuels. Syngas can be converted to liquid fuels, for example, by methanol synthesis, mixed-alcohol synthesis, Fischer-Tropsch chemistry, and syngas fermentation to ethanol. Syngas can also be directly combusted to produce heat and power.

Syngas can also be converted to dimethyl ether (DME), either directly from syngas or through a methanol intermediate. DME is an oxygenated molecule (CH₃—O—CH₃) that is non-toxic, non-carcinogenic, non-corrosive, and clean-burning (little or no soot formation). The energy content of DME, on a weight basis, is over 40% higher than that of methanol. DME has a high cetane number (about 60) and is a known replacement for diesel fuel. In addition to its uses as a fuel, DME can also be used as a propellant.

The market for DME fuels has been slow to develop, particularly in the United States. There is no current infrastructure in place to deploy DME as a liquid-transportation fuel for vehicles. Additionally, pure DME is typically a vapor at ambient conditions, so DME fuel would need to be pressurized in a vehicle tank to provide a sufficient quantity of DME in a single fill. Pure DME needs to be under about 5 bar pressure to be liquefied at room temperature.

On the other hand, there is an existing market for distributing and utilizing cylinder fuels for residential use, such as for cooking and heating; and for portable use, such as during camping, hiking, and the like. The rise in popularity of light-weight equipment for extended backpacking, and the increasing restrictions on campfires in wilderness areas, have made small cooking and heating devices popular.

In view of the beneficial fuel properties of DME, while recognizing certain thermodynamic limitations of DME, what are needed are new fuel compositions that contain DME, methods of making the fuel compositions, methods of using the fuel compositions, apparatus for making and using the fuel compositions, and systems relating to the foregoing. Preferably, these new fuel compositions are produced substantially from renewable resources, such as biomass, to provide green fuel compositions, methods, and systems.

SUMMARY OF THE INVENTION

In some variations, the present invention provides a fuel composition comprising dimethyl ether and a C₂ or larger alcohol. For example, the alcohol may be selected from ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, and/or tert-butanol.

In these or other variations, the invention provides a fuel composition comprising dimethyl ether and a C₂ or larger hydrocarbon. For example, the hydrocarbon may be selected from ethane, ethylene, propane, propylene, propyne, propadiene, 1-butane, isobutane, isobutylene, 1-butene, 2-butene, and/or 1,3-butadiene.

The invention also provides methods of producing a fuel composition, the method comprising:

(a) converting a first amount of syngas into dimethyl ether;

(b) providing a C₂ or larger alcohol;

(c) combining at least a portion of the dimethyl ether with the alcohol, thereby producing a fuel composition,

wherein the alcohol is in a concentration of at least 1 wt %.

The invention additionally provides methods of producing a fuel composition, the method comprising:

(a) converting a first amount of syngas into dimethyl ether;

(b) providing a C₂ or larger hydrocarbon; and

(c) combining at least a portion of the dimethyl ether with the hydrocarbon, thereby producing a fuel composition,

wherein the dimethyl ether is in a concentration of at least 10 wt %.

In some variations, this invention provides a method of using a mixture comprising (i) dimethyl ether and (ii) a hydrocarbon or alcohol having at least two carbon atoms, the method comprising introducing the mixture and an oxidant to a burner under suitable conditions for combustion of at least a portion of the mixture.

In other variations, the invention provides a method of using a mixture comprising (i) dimethyl ether and (ii) a hydrocarbon or alcohol having at least two carbon atoms, the method comprising introducing the mixture and an oxidant to a catalyst surface under suitable conditions for catalytic, flameless oxidation of at least a portion of the mixture.

In still other variations, the invention provides a method of using a mixture comprising (i) dimethyl ether, (ii) a hydrocarbon or alcohol having at least two carbon atoms, and (iii) water, the method comprising introducing the mixture and an oxidant to a fuel cell under suitable conditions for oxidation of at least a portion of the dimethyl ether and/or at least a portion of the hydrocarbon or alcohol, to generate electrical power.

In yet other variations, the invention provides a method of using a mixture comprising (i) dimethyl ether and (ii) a hydrocarbon or alcohol having at least two carbon atoms, the method comprising introducing a primary fluid and the mixture, as a propellant for the primary fluid, to a container or chamber.

In certain variations, the invention provides a method of using a mixture comprising (i) dimethyl ether and (ii) a hydrocarbon or alcohol having at least two carbon atoms, the method comprising introducing the mixture, as a refrigerant, to a refrigeration cycle.

The present invention also provides apparatus, systems, and kits. For example, in some embodiments, a system of the invention includes:

(a) a container adapted for containing a mixture comprising dimethyl ether, and a hydrocarbon or alcohol;

(b) a burner adapted for receiving the mixture from the container, and for receiving an oxidant, to oxidize at least a portion of the mixture, thereby generating heat and/or light; and

(c) a heating and/or lighting region for conveying the heat and/or light to a user.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

This description will enable one skilled in the art to make and use the invention, and it describes several embodiments, adaptations, variations, alternatives, and uses of the invention, including what is presently believed to be the best mode of carrying out the invention.

As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly indicates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this invention belongs. As used herein, a “composition,” “blend,” or “mixture” are all intended to be used interchangeably.

Unless otherwise indicated, all numbers expressing parameters, conditions, concentrations, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending at least upon a specific analytical technique.

Some aspects of the present invention are premised on the realization that DME fuels can be improved by the addition of certain other chemicals to the DME. The improvements may relate to the resulting chemical properties of the fuel blend, the economics of the selection of fuels in the blend, environmental benefits associated with the source of the fuels selected for the blend, or various consumer benefits associated with the blend.

In some variations, a fuel composition comprises dimethyl ether and a C₂ or larger alcohol (“C₂₊ alcohol”). As intended herein, an “alcohol” means any hydrocarbon with at least one hydroxyl group bonded to a carbon atom. Alcohols include primary, secondary or tertiary alcohols, based upon the number of carbon atoms connected to the carbon atom that bears the hydroxyl group. The C₂₊ alcohol may be linear, branched, cyclic, or aromatic, and may contain carbon-carbon double or triple bonds. As is known, the number of structural isomers increases significantly as the carbon number of the alcohol increases.

In some embodiments, the fuel composition comprises an alcohol selected from C₂ to C₁₂ alcohols, such as C₂, C₃, C₄, C₅, or C₆ alcohols. For example, the alcohol may be selected from ethanol, 1-propanol (also known as n-propanol), 2-propanol (also known as isopropyl alcohol), 1-butanol (also known as n-butanol), 2-butanol (also known as sec-butanol), isobutanol, or tert-butanol.

The concentration of the alcohol may vary within the fuel composition. Generally speaking, the alcohol concentration may be selected to optimize one or more fuel properties, and/or for economic reasons. Fuel properties may relate, for example, to energy content (lower heating value or higher heating value), vapor pressure, boiling point, autoignition temperature, flash point, or gel point. Fuel properties for adjustment or optimization may also relate to solution thermodynamics, such as the ability to maintain a single phase wherein the alcohol and DME are co-solvents.

In some embodiments, the fuel composition comprises the C₂₊ alcohol in a concentration of at least 1 wt %, or at least 10 wt %, such as about 15, 20, 25, 30, 35, 40, or 45 wt %. In certain embodiments, the C₂₊ alcohol is present in a concentration of at least 50 wt %.

For example, a fuel composition may consist essentially of 50 wt % DME and 50 wt % isobutanol. As used herein, the phrase “consist essentially of” is intended to refer to fuel species present in the fuel composition, and excludes any additives. As another example, a fuel composition may consist essentially of 80 wt % DME and 20 wt % ethanol, or 35 wt % DME and 65 wt % 2-propanol.

Certain fuel compositions may include additional alcohols, which may be selected from any alcohols (including methanol). In some embodiments, the additional alcohol(s) are selected from methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, or tert-butanol.

In some variations, a fuel composition comprises dimethyl ether and a C₂ or larger hydrocarbon (“C₂₊ hydrocarbon”), such as a C₂ to C₁₀ hydrocarbon. As intended herein, a “hydrocarbon” means any organic molecule consisting of carbon and hydrogen. Hydrocarbons include saturated hydrocarbons (alkanes), which may be linear or branched; unsaturated hydrocarbons having one or more double bonds (alkenes, or olefins) or triple bonds (alkanes) between carbon atoms; cycloalkanes containing one or more carbon rings to which hydrogen atoms are attached; and aromatic hydrocarbons, also known as arenes, that have at least one aromatic ring. Depending primarily on the molecular weight, hydrocarbons can be gases, liquids, waxes, oligomers, or polymers.

In some embodiments, the fuel composition comprises ethane and/or ethylene. In some embodiments, the fuel composition comprises one or more C₃ hydrocarbons selected from propane, propylene, propyne, or propadiene. In these or other embodiments, the fuel composition comprises one or more C₄ hydrocarbons selected from n-butane, isobutane, isobutylene, 1-butene, 2-butene, or 1,3-butadiene.

In some embodiments, the fuel composition comprises a C₅ to C₁₀ hydrocarbon, such as n-pentane, cyclohexane, or isooctane. In certain embodiments, the fuel composition does not include C₃ hydrocarbons, C₄ hydrocarbons, or both C₃ and C₄ hydrocarbons. Some fuel compositions do not include liquefied petroleum gas.

The concentration of the hydrocarbon may vary within the fuel composition. Generally speaking, the hydrocarbon concentration may be selected to optimize one or more fuel properties, and/or for economic reasons. Fuel properties may relate, for example, to energy content (lower heating value or higher heating value), vapor pressure, boiling point, autoignition temperature, flash point, or gel point.

In some embodiments, the fuel composition comprises DME in a concentration of at least 10 wt %. DME may be present in a concentration of at least 20 wt %, such as about 25, 30, 35, 40, 45, 50 wt % or more, in various embodiments. In these or other embodiments, the fuel composition may include one or more hydrocarbons in a hydrocarbon concentration from about 10 wt % to about 80 wt %, such as about 20, 30, 40, 50, 60, or 70 wt %.

For example, a fuel composition may consist essentially of 50 wt % DME and 50 wt % isobutane. As another example, a fuel composition may consist essentially of 70 wt % DME and 30 wt % ethane, or 25 wt % DME and 75 wt % 1,3-butadiene.

Some embodiments include two, three, four, five, or more unique hydrocarbon species in a fuel mixture with DME. These additional hydrocarbons may be selected from methane, ethane, ethylene, propane, propylene, propyne, propadiene, 1-butane, isobutane, isobutylene, 1-butene, 2-butene, or 1,3-butadiene, for example. When additional hydrocarbons are employed, the relative proportions of the hydrocarbons within the blend with DME may vary.

Certain embodiments provide a fuel composition comprising DME, a C₂₊ hydrocarbon, and a C₂₊ alcohol. The alcohol may be selected from ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, or tert-butanol. When a fuel composition includes a hydrocarbon and an alcohol, each of the hydrocarbon and alcohol may be present (independently) in a concentration of at least 1 wt %, such as at least 10 wt %, along with DME and any other components that may be in the mixture.

Some fuel compositions of the invention further include water, either as unintentional moisture or as an intended concentration of water in the fuel mixture. In some embodiments, water is present in an amount from about 0.01 wt % to about 10 wt %, such as from about 0.1 wt % to about 1 wt %.

The fuel compositions of the invention may include any number of additional fuel components or fuel additives. For example, the fuel compositions may include various stabilizers, lubricants, and/or the additives. In preferred embodiments, the selected fuel composition with DME and either (or both) of C₂₊ alcohols or C₂₊ hydrocarbons is relatively stable without the need for an additional fuel stabilizer.

In some embodiments, the fuel composition further comprises at least one fuel additive to adjust the color or appearance of the mixture. For example, colorants or dyes may be added to the composition to impart a certain color, such as green or blue, to distinguish the fuel in the market.

In some embodiments, the fuel composition further comprises at least one fuel additive to adjust the scent or aroma of the mixture. For example, a pine fragrance oil or derivatives of pinene (e.g., catalytically oxidized pinene) may be utilized to impart a pine scent to the fuel compositions.

Additionally, various unintentional impurities may be present in any fuel compositions provided herein. Impurities include solids (e.g., dust and dirt particles, or metals), liquids (e.g., water, degradation products, or reaction products from fuel species), or vapors (e.g., air or carbon dioxide). These impurities may be introduced during the initial production of the mixture, or during storage, distribution, or consumer use.

Variations of the present invention relate to methods of making certain fuel compositions. In some variations, a method of producing a fuel composition comprises: (a) converting a first amount of syngas (CO and H₂) into DME; (b) providing a C₂ or larger alcohol; (c) combining at least a portion of the DME with the alcohol, thereby producing a fuel composition with an alcohol in a concentration of at least 1 wt %, such as about 5, 10, 20, 30, 40, 50 wt % or higher.

The alcohol is a linear or branched C₂ to C₆ alcohol, in some embodiments, such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, or tert-butanol. Additional alcohols, including methanol, may further be included in the fuel composition.

Step (a) produces DME from syngas. There are several methods known in the art to convert syngas to DME. One option is to employ a two-step process, wherein syngas is first converted to methanol, and then the methanol is dehydrated to DME (two moles of methanol convert to one mole of DME plus one mole of water). Typically, fixed-bed reactors are employed for the methanol synthesis and dehydration reactions, but other types reactors may be used. Catalysts for converting syngas to methanol are known, such as catalysts that include a mixture of copper, zinc oxide, and alumina. Catalysts for dehydrating methanol to DME include solid-acid catalysts, such as various forms of alumina and silica.

Another option for step (a) is to employ a one-step route, wherein syngas is directly converted, catalytically, into DME. A fixed-bed or slurry reactor may be employed, for example. Although there are potential cost and yield advantages with the one-step route, management of heat and recycle streams is regarded as more complex compared to the two-step route. Reference is made to Peng et al., “Single-Step Syngas-to-Dimethyl Ether Processes for Optimal Productivity, Minimal Emissions, and Natural Gas-Derived Syngas,” Ind. Eng. Chem. Res., Vol. 38, No. 11, 1999, incorporated by reference for its teachings regarding syngas conversion to DME.

The specific source of syngas, including the feedstock type and the syngas-generation method (discussed below), may influence the selection of the DME production method. For direct synthesis, it may be desirable for the syngas to have a H₂/CO ratio of about 1. In a two-step route through methanol, syngas with a H₂/CO ratio of about 2 is generally preferred, for stoichiometric conversion of syngas to methanol.

Step (b) which provides an alcohol may include receiving some or all of the alcohol for use in the method. That is, an alcohol may be purchased or otherwise acquired (e.g., in a trade) by the person or entity carrying out the method of making the fuel composition.

In other embodiments, step (b) includes converting a second amount of syngas into an alcohol. The syngas to produce the alcohol may be from the same source of syngas as that used to produce the DME, or it may be from a different feedstock within the same plant, or from a different source or location.

Step (b) may provide an alcohol via catalytic conversion of the second amount of syngas into an alcohol. For example, an alcohol-synthesis catalyst can be employed to produce mixed alcohols, such as C₂ to C₅ alcohols, from syngas. Suitable catalysts may include, but are not limited to, those disclosed in co-pending and commonly assigned U.S. patent application Ser. No. 12/166,167. Exemplary catalysts for syngas conversion to alcohols include Co, Mo, Cu, Zn, Rh, Ti, Fe, Ir, ZnO/Cr₂O₃, Cu/ZnO, CuO/CoO, Co/S, Mo/S, Co/Mo/S, Ni/S, Ni/Mo/S, Ni/Co/Mo/S, Rh/Ti, Rh/Mn, Rh/Ti/Fe/Ir, and mixtures thereof. The addition of basic promoters (e.g., K, Li, Na, Rb, Cs, and Fr) increases the activity and selectivity of some of these catalysts for C₂₊ alcohols.

Alternatively, or additionally, step (b) may include biological conversion of syngas into an alcohol, preferably a C₂ to C₄ alcohol, by syngas fermentation with a suitable microorganism. Bioconversion of CO or H₂/CO₂ to ethanol or butanol is well known. For example, syngas biochemical pathways and energetics of such bioconversions are summarized by Das and Ljungdahl, “Electron Transport System in Acetogens” and by Drake and Kusel, “Diverse Physiologic Potential of Acetogens,” appearing respectively as Chapters 14 and 13 of Biochemistry and Physiology of Anaerobic Bacteria, L. G. Ljungdahl eds., Springer (2003).

Any suitable microorganisms may be utilized that have the ability to convert CO, H₂, or CO₂, individually or in combination with each other or with other components that are typically present in syngas. Anaerobic bacteria, such as those from the genus Clostridium, have been demonstrated to produce ethanol from CO, H₂, or CO₂ via the acetyl CoA biochemical pathway. Generally speaking, microorganisms suitable for syngas fermentation to C₂₊ alcohols may be selected from genera including Clostridium, Moorella, Carboxydothermus, Acetogenium, Acetobacterium, Butyribacterium, Peptostreptococcus, and Geobacter. Microorganism species suitable for syngas fermentation may be selected from Clostridium ljungdahli, Clostridium autoethanogenum, Clostridium ragsdalei, Clostridium carboxidivorans, Butyribacterium methylotrophicum, Eurobacterium limosum, and genetically engineered, mutated, or evolved variations thereof.

In preferred embodiments, the first amount of syngas (for making the DME) is generated from a biomass feedstock. In some embodiments wherein the alcohol is produced from syngas conversion as part of the method, the second amount of syngas is also generated from a biomass feedstock. The first and second amounts of syngas are optionally generated from a common biomass feedstock at a single location, or at co-located manufacturing sites.

The resulting fuel composition preferably includes at least 20%, more preferably at least 50%, such as 80%, 95%, or even more, renewable carbon content. By “renewable carbon” it is meant that the carbon atoms in the fuel mixture are derived from a renewable feedstock, such as (but by no means limited to) lignocellulosic biomass.

In some embodiments, an alcohol is produced from one or more sugars contained in a biomass feedstock. Cellulosic biomass contains C₅ sugars, such as xylose and arabinose, and C₆ sugars, such as glucose, galactose, and mannose, which may be recovered from the biomass, such as by acid or enzymatic hydrolysis of the cellulose and hemicellulose chains, to form the sugar monomers. The C₅ and C₆ sugars may then be converted to alcohols by fermentation, using well-known techniques and microorganisms (including natural or modified bacteria or yeast).

When more than one alcohol is included in the fuel composition with DME, the different alcohols may be produced or provided from different techniques or sources. For example, a first alcohol could be ethanol produced from syngas fermentation while a second alcohol could be methanol produced from syngas catalytic conversion. Or, a first alcohol could be isobutanol provided by (and received from) a third party while a second alcohol could be ethanol produced from glucose fermentation, the glucose being derived from the same type of feedstock as that used to generate the syngas for DME synthesis.

In other variations of the invention, a method of producing a fuel composition comprises: (a) converting a first amount of syngas into DME; (b) providing a C₂ or larger hydrocarbon; and (c) combining at least a portion of the DME with the hydrocarbon, thereby producing a fuel composition with DME in a concentration of at least 10 wt %, such as about 15, 20, 30, 40, 50 wt % or higher. In some embodiments, the concentration of the hydrocarbon is from about 10 wt % to about 80 wt %, such as about 15, 20, 30, 40, or 50 wt %.

The hydrocarbon is a C₂ to C₄ hydrocarbon, in some embodiments, such as ethane, ethylene, propane, propylene, propyne, propadiene, 1-butane, isobutane, isobutylene, 1-butene, 2-butene, or 1,3-butadiene. Additional hydrocarbons, including methane, may further be included in the fuel composition. In some embodiments, the hydrocarbon is a C₅ to C₁₀ hydrocarbon, such as n-pentane, cyclohexane, or isooctane. An additional hydrocarbon, including methane, may further be included.

Step (b) which provides a hydrocarbon may include receiving some or all of the hydrocarbon for use in the method. That is, a hydrocarbon may be purchased or otherwise acquired (e.g., in a trade) by the person or entity carrying out the method of making the fuel composition.

In other embodiments, step (b) includes converting a second amount of syngas into a C₂₊ hydrocarbon. The syngas to produce the hydrocarbon may be from the same source of syngas as that used to produce the DME, or it may be from a different feedstock within the same plant, or from a different source or location.

Step (b) may include catalytic conversion of the second amount of syngas into a hydrocarbon. For example, the well-known Fischer-Tropsch process can be employed to produce hydrocarbons, such as C₅₊ hydrocarbons, from syngas. Catalysts known to be active for Fischer-Tropsch chemistry include, but are not limited to, cobalt, iron, nickel, and ruthenium. In addition to the active metal, these catalysts typically contain a number of promoters, such as potassium and/or copper. Fischer-Tropsch catalysts are usually supported on high-surface-area supports such as silica, alumina, or zeolites.

When branched C₄ hydrocarbons are specifically desired, syngas may be converted into isobutane and/or isobutylene by isosynthesis of syngas. The isosynthesis reactions can convert syngas to isobutane and isobutylene under relatively extreme reaction conditions, using a thorium-based or zirconium-based catalyst, for example. Isosynthesis is selective to iso-C₄ hydrocarbons and only trace amounts of oxygenates are typically formed. The specific catalyst and conditions may be selected to adjust the ratio of isobutane to isobutylene. Various promoters may improve the activity and selectivity.

In preferred embodiments, the first amount of syngas (for making the DME) is generated from a biomass feedstock. In some embodiments wherein the hydrocarbon is produced from syngas conversion as part of the method, the second amount of syngas is also generated from a biomass feedstock. The first and second amounts of syngas are optionally generated from a common biomass feedstock at a single location, or at co-located manufacturing sites.

The method used to produce syngas is not particularly limited. Carbon-containing feedstocks may be converted to syngas by gasification, for example. Gasification requires an oxidant, commonly air, high-purity oxygen, steam, or some mixture of these gases. Common gasifier configurations include fixed-bed updraft, fixed-bed downdraft, bubbling fluidized bed, and circulating fluidized bed.

Syngas can also be produced by pyrolysis, devolatilization, steam reforming, and partial oxidation of one or more feedstocks recited herein. In some embodiments, syngas is produced according to methods described in Klepper et al., “Methods and apparatus for producing syngas,” U.S. patent application Ser. No. 12/166,167 (filed Jul. 1, 2008), the assignee of which is the same as the assignee of the present application. U.S. patent application Ser. No. 12/166,167 is incorporated by reference herein in its entirety.

The syngas may be produced from a wide range of feedstocks of various types, sizes, and moisture contents. “Biomass,” for the purposes of the present invention, is any material not derived from fossil resources and comprising at least carbon, hydrogen, and oxygen. Biomass includes, for example, plant and plant-derived material, vegetation, agricultural waste, forestry waste, wood waste, paper waste, animal-derived waste, poultry-derived waste, and municipal solid waste. Other exemplary feedstocks include cellulose, carbohydrates, biochar, and charcoal.

In various embodiments of the invention utilizing biomass to produce syngas, the biomass feedstock may include one or more materials selected from: timber harvesting residues, softwood chips, hardwood chips, tree branches, tree stumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover, wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus, animal manure, municipal garbage, municipal sewage, commercial waste, grape pumice, almond shells, pecan shells, coconut shells, coffee grounds, grass pellets, hay pellets, wood pellets, cardboard, paper, plastic, and cloth.

The syngas may alternatively, or additionally, be produced from carbon-containing feedstocks other than biomass, such as a fossil fuel (e.g., coal or petroleum coke), or any mixtures of biomass and fossil fuels. Any method, apparatus, or system described herein can be used with any carbonaceous feedstock. Also, various mixtures may be utilized, such as mixtures of biomass and coal.

Selection of a particular feedstock or mixture of feedstocks is not regarded as technically critical, but is carried out in a manner that tends to favor an economical process and business system, preferably including consideration of the net renewable carbon content in the resulting fuel compositions. In various embodiments of this invention, the fuel composition preferably includes at least 20%, more preferably at least 50%, such as 80%, 95%, or even more, renewable carbon content.

In some embodiments, syngas is produced or otherwise provided in a biorefinery. The syngas may be divided into a plurality of streams and fed to several unit operations. Biorefinery optimization may be carried out to adjust the splits to the different units, for economic reasons. At least a portion of the syngas, in the context of the present invention, is converted to liquid fuels.

The syngas may alternatively, or additionally, be provided by a third party for conversion into DME and optionally into hydrocarbons and/or alcohols. Syngas may be received from a third party via pipeline, portable tanks or cylinders, trucks, rail, or by any other known means of transporting syngas.

In some embodiments, a C₂ to C₁₀ hydrocarbon is produced from one or more sugars contained in a biomass feedstock. Cellulosic biomass contains C₅ sugars, such as xylose and arabinose, and C₆ sugars, such as glucose, galactose, and mannose, which may be recovered from the biomass, such as by acid or enzymatic hydrolysis of the cellulose and hemicellulose chains, to form the sugar monomers. The C₅ and C₆ sugars may then be converted to hydrocarbons by known catalytic techniques, including catalytic hydrotreating and catalytic condensation processes, such as base-catalyzed condensation, acid-catalyzed dehydration, and alkylation reactions.

When more than one hydrocarbon is included in the fuel composition with DME, the different hydrocarbons may be produced or provided from different techniques or sources. For example, a first hydrocarbon could be n-hexane produced from catalytic conversion of syngas while a second hydrocarbon could be methane produced from biomass gasification. Or, a first hydrocarbon could be isobutane produced from syngas isosynthesis while a second hydrocarbon could be propane provided by (and received from) a third party.

In these methods, step (c) may include calculating and optionally adjusting, by varying the fuel composition, one or more properties selected from lower heating value, higher heating value, vapor pressure, boiling point, autoignition temperature, flash point, or gel point.

In any of these methods, an optional step includes introducing one or more additives selected from fuel stabilizers, lubricants, colorants, odorants, or any other fuel or chemical additives. Additives may contribute functionally, ornamentally, or some combination of these, to the fuel composition.

Additional variations of this invention relate to methods of using certain fuel compositions, and to commercial applications and systems for such compositions. In some variations, a method of using a mixture comprising (i) DME and (ii) a hydrocarbon or alcohol, includes introducing the mixture and an oxidant to a burner under suitable conditions for combustion of at least a portion of the mixture.

The hydrocarbon or alcohol may be selected from molecules having at least two carbon atoms, in some embodiments, including any of the compositions described herein. For example, a hydrocarbon, if present, may be selected from ethane, ethylene, propane, propylene, propyne, propadiene, 1-butane, isobutane, isobutylene, 1-butene, 2-butene, and 1,3-butadiene. An alcohol, if present, may be selected from ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, or tert-butanol. The mixture may include both a hydrocarbon and an alcohol. The oxidant will typically be air, although other oxidants such as oxygen or oxygen-enriched air, may be employed as well.

In some embodiments, the combustion is intended primarily to provide a source of heat. The heat may be utilized for raising a local temperature for a user, such as for warming up a room or a piece of equipment (e.g., a heating mantle). Or, the heat may be utilized for heating up or cooking a liquid or solid substance for consumption, or other purposes. The burner may be adapted for a stationary cooking stove or a portable camping stove, for example.

In some embodiments, the combustion is intended primarily to provide a source of light. The light may be utilized for lighting up a room, a trail, or a camping site, for example. The burner may be adapted, in some embodiments, for a camping lantern or similar device intended to provide light (and optionally, heat). Because DME flames are usually blue, the addition of one or more hydrocarbons or alcohols into the fuel mixture may cause the flame to contain colors having more usable light (e.g., white, yellow, or orange light) when light output is desired.

In some embodiments, the combustion is intended primarily to provide a source of power (i.e., usable energy over a period of time). The power may be utilized in various stationary or portable applications, and may be utilized in both consumer and industrial settings. For example, the combustion of the fuel mixture may provide power for a hand-held pump or a personal water-purification device for camping. In a different example, the burner may be adapted for a vehicle combustion chamber, wherein the composition is used as a transportation fuel or fuel additive.

Other variations are premised on the realization that flameless oxidation may be achieved with a suitable catalyst capable of oxidizing the fuel mixture in the presence of an oxidant. In some variations, a method of using a mixture comprising (i) DME and (ii) a hydrocarbon or alcohol, includes introducing the mixture and an oxidant to a catalyst surface under suitable conditions for catalytic, flameless oxidation of at least a portion of the mixture.

The catalytic oxidation may provide a source of heat, such as for a cooking stove or camping stove, and/or a source of light, such as for a camping lantern. Many known catalysts are suitable for catalytic complete oxidation, such as (but not limited to) Pt, Pd, Rh, Re, Fe, and Sn, with various supports and promoters. The oxidation catalyst can take the form of a powder, pellets, granules, beads, extrudates, and so on. When a catalyst support is optionally employed, the support may assume any physical form such as pellets, spheres, monolithic channels, etc. The oxidation catalyst may be provided in various reactor configurations, such as in a microchannel reactor.

Still other variations provide a method of using a mixture comprising (i) dimethyl ether, (ii) a hydrocarbon or alcohol, and (iii) water, the method comprising introducing the mixture and an oxidant to a fuel cell under suitable conditions for oxidation of at least a portion of the DME and/or at least a portion of the hydrocarbon or alcohol, to generate electrical power.

The electrical power from the fuel cell may be utilized in various stationary or portable applications, and may be useful in consumer, industrial, and transportation applications.

Preferably, both the DME and hydrocarbon (or alcohol, when an alcohol is used) are oxidized in the fuel cell. The oxidation kinetics for particular fuel species in a fuel cell may vary due to different mass-transfer rates across membranes (or to/from solid-oxide surfaces), as well as due to different reaction rates at catalyst surfaces. Fuel compositions for fuel cells may be optimized in view of particular fuel cell configurations and systems that employ the fuel cells.

Additional aspects of the present invention are premised on the realization that DME as a propellant or refrigerant can be improved by the addition of certain other chemicals to the DME. The improvements may relate to the resulting chemical properties of the blend, to the economics of the selection of molecules in the blend, or to environmental benefits associated with the source of the materials selected for the blend.

In some variations, a method of using a mixture comprising (i) dimethyl ether and (ii) a hydrocarbon or alcohol, includes introducing a primary fluid and the mixture, as a propellant for the primary fluid, to a container or chamber. The primary fluid may be a fuel or fuel blend, such as diesel or biodiesel fuel. Or, the primary fluid may be a chemical or chemical blend for consumer use, such as an aerosol product.

In other variations, a method of using a mixture comprising (i) dimethyl ether and (ii) a hydrocarbon or alcohol, includes introducing the mixture, as a refrigerant, to a refrigeration cycle. The refrigeration cycle may be adapted for a refrigerator, a freezer, an air conditioner, a heat pump, or a cryogenic apparatus, for example.

Any of these disclosed methods may further include the step of actually providing the mixture for the purpose of using the mixture in an intended manner. The methods, however, do not require that the fuel mixtures be provided by the same person or entity that provides the rest of the components, such as the burner. For example, a fuel mixture may initially be provided in a small cylinder (or canister), with the intent that the cylinder be later refilled, or later replaced with a new cylinder filled with fuel, for repeating the methods of the invention any number of times.

Still other variations of the invention relate to systems, which may include methods and/or apparatus for using DME-based fuel compositions. Some variations provide a system comprising: (a) a container adapted for containing a mixture comprising dimethyl ether and a hydrocarbon or an alcohol; (b) a burner adapted for receiving the mixture from the container, and for receiving an oxidant, to oxidize at least a portion of the mixture, thereby generating heat and/or light; and (c) a heating and/or lighting region for conveying the heat and/or light to a user.

The container may be a rigid container, such as (but not limited to) a cylinder, a tank, or a tube. The container may be fabricated from a metal or metal alloy, such as steel, or from a ceramic, plastic, or other material. The container may be a flexible container, fabricated for example from a polymer. In some embodiments, the container is removable from the system, so that it can be refilled or replaced. In certain embodiments, the container is not readily removed from the system but rather is configured to be refilled, in place, with an additional amount of the fuel mixture. The container may or may not be initially filled with a fuel mixture.

The system includes a burner that may be configured to create a controlled combustion flame, or may be configured with a catalyst to create a flameless oxidation reaction. In principle, a burner could be designed with a catalytic surface or region, so that a portion of the fuel mixture is oxidized in surface reactions while the remainder of the fuel mixture is combusted in a flame front. Such a design could help control the quality of the flame, or could be used to adjust the relative outputs of heat, light, and power, for example.

The heating and/or lighting region for conveying the heat and/or light to a user may take on a wide variety of shapes, sizes, and materials of construction. Heat may be transferred from the burner to a user (or to an object to be heated) through a metal panel, a metal ring, a heat exchanger, or simply through open air, for example. Light may be transferred from the burner to a user through an open window or region of space, a glass panel, or a light reflector, for example.

In some embodiments, the system forms (or is part of) a cooking stove. In certain embodiments, the system forms a camping stove, a camping lantern, or another device for providing an energy source during camping, hiking, backpacking, long-distance cycling, or other outdoor activities.

The system components, and in particular the burner (as will be further discussed below), may be designed or optimized for specific fuels and mixtures, or may instead be designed for greater fuel flexibility. Preferably, the burner is specifically suitable for combustion of mixtures that contain DME, of various concentrations as described herein.

In particular embodiments, the burner is selected, designed, engineered, or adjusted to be suitable for one or more hydrocarbons selected from ethane, ethylene, propane, propylene, propyne, propadiene, 1-butane, isobutane, isobutylene, 1-butene, 2-butene, or 1,3-butadiene; and/or for one or more alcohols selected from ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, or tert-butanol.

A system of the invention may be provided in some form of “kit” which here means any type of package, box, or other means of collecting or storing the components of the system. The kit should include at least a fuel container, a burner, and a heating and/or lighting part or region for conveying heat and/or light to a user. In preferred embodiments, the system includes user instructions that describe the intended use(s) and safety aspects. The user instructions may be in the form of a physical manual, or may be provided by directing a user to a web site, for example. The kit may also include various other items, such as a spare cylinder, spare burner parts, optional components to adjust relative heat, light, or power output, a list of fuel suppliers, environmental, health, and safety information, and marketing material.

This invention also contemplates apparatus configured for a consumer or user to carry out any of the disclosed methods. In some variations, the design of the burner portion of the apparatus will generally follow certain principles as will now be further described. This disclosure incorporates by reference the following textbook, in its entirety: Turns, “An Introduction to Combustion: Concepts and Applications,” McGraw-Hill, Inc., pp. 1-565, 1996.

Fuel compositions will dictate, in part, the possible burner designs. While it may be preferred to design a burner that has wide fuel flexibility, it also may be preferred to design burners for specific, intended fuel compositions, such as the fuel compositions disclosed herein. Additionally, the intended uses of the apparatus should be considered when selecting or designing a burner. In some embodiments, an apparatus is designed in respect of certain properties or characteristics that may depend on the fuel composition as well as on physical dimensions, materials, or equipment constraints. Such properties may include, for example, average or maximum temperature or heat output, average or maximum light output, and equipment-specific flammability limits.

Some burner embodiments employ laminar jet flames, wherein the fuel stream is partially premixed with air. A primary concern in the design of a burner utilizing laminar jet flames is flame geometry, with short flames being typically preferred. In a jet flame, fuel flows along the flame axis and diffuses outward, while the oxidant (e.g., air) diffuses radially inward. The flame surface is nominally defined to be the locus of points where the fuel and oxidant meet in stoichiometric proportions for combustion, i.e., an equivalence ratio of one. The products formed at the flame surface (at least CO₂ and H₂O) diffuse radially inward and outward.

The flame geometry will depend on the physical burner geometry. Burner geometries may be, for example, circular, square, slot, or curved slot. For a given burner geometry, there will be a relationship between the fuel flow rate and the flame length. The quantity of heat (or light) desired, and/or the rate of heating, should be considered when designing for a fuel flow rate or range of flow rates. The flame length may be of secondary importance, although safety aspects should be considered in any design.

Burners may be designed to run slightly lean, slightly rich, or at or near the stoichiometric combustion ratio. Various equivalence ratios may be implemented. The “equivalence ratio” is defined as the ratio of the fuel-to-oxidant ratio to the stoichiometric fuel-to-oxidant ratio. Thus, equivalence ratios greater than one mean that the system is fuel-rich, and ratios less than one indicate the system is fuel-lean, and oxidant-rich.

In some embodiments, the apparatus is designed to premix some air with the fuel before it burns as a laminar jet diffusion flame. This primary aeration, which may be for example between about 20% and 80% of the stoichiometric air requirement, shortens the flames and helps prevents soot from forming. DME is known to have low soot potential, but other components (e.g., C₂₊ alcohols or hydrocarbons) may not have this attribute. Therefore, attention should be paid in the burner design to controlling soot formation.

The formation and destruction of soot is an important feature in some embodiments of the invention. The incandescent soot within the flame is the primary source of the luminosity of the flame. Because DME burns so cleanly, the flame tends to be blue. For lighting applications (e.g., camping lanterns), blue flames may be a less preferable source of light than orange, yellow, or red flames. In this context, the addition of a hydrocarbon or alcohol to DME allows for the creation of a light source that may be more appealing to a user. Note, however, that the invention is not limited to any particular color of light generated by combustion of the fuel mixtures. In certain embodiments, colors such as blue or green may be desired.

Fuel/oxidant flow regimes may be, for example, momentum-controlled, buoyancy-controlled, or transitional. To determine whether a flame is momentum- or buoyancy-controlled, the flame “Froude number” may be evaluated. The Froude number physically represents the ratio of initial jet momentum flow to the buoyant force experienced by the flame. Thus, a Froude number well in excess of one indicates momentum control, while a Froude number much less than one indicates buoyancy control.

In preferred burner designs, a stable flame is anchored at a desired location and is resistant to flashback, liftoff, and blowoff over the burner's operating range. To hold and stabilize a flame, the design principle is that the local flame speed (whether laminar or turbulent) should substantially match the local mean flow velocity. Design features that may follow this principle include low-velocity bypass ports, refractory burner tiles, flameholders, swirl or jet-induced recirculating flows, or a rapid increase in flow area.

Fuels with high diffusivities are more prone to flashback, whereby the flame propagates upstream, back toward the fuel source. DME has a high diffusivity, and is therefore susceptible to flashback. DME blends with hydrocarbons and alcohols may be optimized specifically to reduce or avoid flashback for a particular burner design. One way to reduce flashback is to design for high flame-propagation speeds.

Flame-propagation speeds may be designed to be relatively high by including a pump or compressor, for either or both of the fuel or oxidant. For example, an electrical air pump may be utilized to pump air through a fuel source, thereby pushing the fuel to the burner, optionally with a metering valve. Or, a small hand pump may be utilized to pump fuel and/or air to the burner. In preferred embodiments, a fuel cylinder of sufficient pressure is employed to drive the fuel to the burner at sufficient velocities.

Generally speaking, burners may be designed for a liquid fuel supply, a vapor fuel supply, or a combination of these. A combination burner, in this context, may refer to a dual design where either a liquid or a vapor may be fed. A combination burner may also mean that a multiphase fuel can be introduced.

Thermodynamically, in a flame, any liquid fuel must first vaporize and heat up before it can combust. Thus, if the fuel is a liquid, a heater may be included to vaporize the fuel before it reaches the flame, and preferably before premixing with the oxidant. For example, an electrical heating element or a small burner (which may operate with the same or a different fuel supply) may be included.

In some embodiments, the vapor pressure of the fuel is sufficiently high such that vaporized fuel is continually fed to the burner. It is also possible, when the fuel is a liquid, to introduce it to the burner using a spray, mist, or droplet injection, such that the liquid is quickly vaporized within the flame itself. A liquid spray or liquid mist may include some amount of vapor, as will be appreciated, dictated by complex mass and heat transfer within a vaporizing drop or particle.

The range of fuel compositions described in the present invention include mixtures that are vapor at room temperature (or typical outdoor temperatures), and some mixtures that are liquid at these temperatures. When the fuel is normally a vapor, it is preferably filled into a pressurized container so that it is present in liquid form (some vapor will usually also be present). Additionally, certain compositions described herein may be present in a multiphase solution, which may be a vapor and a liquid, or even two liquid phases.

Some burners further include a flame igniter. It is possible, but typically not preferable, to ignite a flame with a match or separate flame initiated by a user. A piezoelectric device may be included to cause ignition. Such a device utilizes the mechanical work done by the user in depressing a button to create an electric spark. Other flame igniters may be employed, such as direct or indirect solar-powered igniters.

Various means of controlling the apparatus, and burner, may be included. For example, features may be included to control the fuel flow or pressure, the oxidant flow, the flame output, the temperature of a heating region, and so on. Some form of automating the length of time for burning may be included, such as when a user may not be present to shut down the device.

Many of the aforementioned design principles for laminar flames will also apply for turbulent flows. Turbulent flames are common in larger devices including internal combustion engines, gas turbines, furnaces, and boilers. Such applications often involve—and allow the budget for—highly complicated design features.

For example, engineered fuel injectors may be employed to efficiently deliver fuel mixtures to burners or combustion chambers. Some embodiments include nozzles, i.e. mechanical devices designed to control the direction or characteristics of a fluid flow as it enters an enclosed chamber or pipe via an orifice. Nozzles are capable of reducing the fuel droplet size to generate a fine spray. Nozzles may be selected from atomizer nozzles, swirl nozzles which inject the liquid tangentially, etc. In some embodiments, screens, ceramic filters, or molecular sieves are included to help form small droplets.

In this detailed description, reference has been made to multiple embodiments of the invention and non-limiting examples relating to how the invention can be understood and practiced. Other embodiments that do not provide all of the features and advantages set forth herein may be utilized, without departing from the spirit and scope of the present invention. This invention incorporates routine experimentation and optimization of the methods and systems described herein. Such modifications and variations are considered to be within the scope of the invention defined by the claims.

All publications, patents, and patent applications cited in this specification are herein incorporated by reference in their entirety as if each publication, patent, or patent application were specifically and individually put forth herein.

Where methods and steps described above indicate certain events occurring in certain order, those of ordinary skill in the art will recognize that the ordering of certain steps may be modified and that such modifications are in accordance with the variations of the invention. Additionally, certain of the steps may be performed concurrently in a parallel process when possible, as well as performed sequentially. For example, an integrated process may be employed wherein syngas is converted to DME as well as hydrocarbons and/or alcohols in the same reactor(s).

Therefore, to the extent there are variations of the invention, which are within the spirit of the disclosure or equivalent to the inventions found in the appended claims, it is the intent that this patent will cover those variations as well. The present invention shall only be limited by what is claimed. 

What is claimed is:
 1. A fuel composition comprising dimethyl ether and a C₂ or larger alcohol.
 2. The fuel composition of claim 1, said composition comprising an alcohol selected from C₂ to C₆ alcohols.
 3. The fuel composition of claim 2, wherein said alcohol is selected from the group consisting of ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, tert-butanol, and combinations thereof.
 4. The fuel composition of claim 1, said composition comprising said alcohol in a concentration of at least 1 wt %.
 5. The fuel composition of claim 4, said composition comprising said alcohol in a concentration of at least 10 wt %.
 6. The fuel composition of claim 5, said composition comprising said alcohol in a concentration of at least 50 wt %.
 7. The fuel composition of claim 1, said composition further comprising a second alcohol.
 8. The fuel composition of claim 7, wherein said second alcohol is selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, tert-butanol, and combinations thereof.
 9. The fuel composition of claim 8, wherein said second alcohol is methanol.
 10. The fuel composition of claim 1, wherein said fuel composition includes 95% or more renewable carbon content.
 11. A fuel composition comprising dimethyl ether and a C₂ or larger hydrocarbon.
 12. The fuel composition of claim 11, said composition comprising a hydrocarbon selected from C₂ to C₁₀ hydrocarbons.
 13. The fuel composition of claim 12, said composition comprising ethane and/or ethylene.
 14. The fuel composition of claim 12, said composition comprising one or more C₃ hydrocarbons selected from the group consisting of propane, propylene, propyne, and propadiene.
 15. The fuel composition of claim 12, said composition comprising one or more C₄ hydrocarbons selected from the group consisting of n-butane, isobutane, isobutylene, 1-butene, 2-butene, and 1,3-butadiene.
 16. The fuel composition of claim 12, said composition comprising a C₅ to C₁₀ hydrocarbon.
 17. The fuel composition of claim 11, wherein said composition does not include liquefied petroleum gas.
 18. The fuel composition of claim 11, said composition comprising said dimethyl ether in a concentration of at least 10 wt %.
 19. The fuel composition of claim 18, said composition comprising said dimethyl ether in a concentration of at least 50 wt %.
 20. The fuel composition of claim 11, wherein said fuel composition includes 95% or more renewable carbon content. 